1. Field of the Invention
This invention relates to a system and method for examining the tissue of an object to be investigated and is especially directed to in vivo measurement of the sound velocity of the tissue. Through such measurement, the user of the system and method can determine the nature of the tissue and often perform medical or scientific diagnosis.
2. Description of the Prior Art
Nishimura N. et al., "Measurement of Sound Velocity as a Diagnostic Tool Diffuse Liver Diseases," Japanese Journal of Medical Ultrasonics, 44-B-5, May 1984 shows a technique of measuring sound velocity of liver with two single transducers disposed at both ends of a linear array transducer. These two single transducers are disposed so that their beams cross within the liver. An ultrasonic pulse and its echo propagate from one single transducer through that cross point and to the other transducer. The propagation time taken by the pulse to travel that path is measured. The average sound velocity through the propagation path is computed from the propagation time, the distance between the two transducers, and the angles of propagation defined by the placement of the transducers. In this past technique, however, it is difficult to measure different paths of travel without physically moving one or both transducers. It is also difficult to achieve good contact with the surface of the object because the single transducers cannot be laid flat against the surface of the objects being investigated but instead must be angled. This problem becomes worse whenever the intersection point of the transducer's axes is near one or both transducers.